The invention relates to a combination of positron emission tomography and magnetic resonance tomography units (PET/MRT unit) for imaging an examination object in an examination space. The invention also relates to a method for imaging an examination object in an examination space by a combined positron emission tomography and magnetic resonance tomography unit.
Magnetic resonance tomography (MRT) and positron emission tomography (PET) are nowadays indispensable methods for the accurate diagnosis of many diseases and medical disturbances. It is possible hereby to image affected organs and organ parts exactly in three dimensions and, moreover, to track the physiological and biochemical processes in the affected organs or organ parts down to a molecular plane.
The strength of MRT resides in the ability to image many organs exactly with a very high degree of spatial resolution. By comparison with computed tomography (CT), this method manages here without potentially injurious ionizing radiation. By contrast, the strengths of PET reside chiefly in the functional imaging, that is to say in the imaging of biochemical and physiological processes. However, PET has a comparatively poor spatial resolution of, for example, approximately 5 mm that can no longer be raised without additional radiation loading. By combining the two methods, it is possible to use both the high spatial resolution of MRT and the functional information from PET toward an even more exact diagnosis.
Combined CT and PET measurements are already known to the specialists in the field. In this case, a patient is conveyed directly in sequence through the detector ring of a CT unit and the detector ring of a PET unit. The resulting images are merged in a computer. Similar considerations apply to positron emission tomography and magnetic resonance tomography. In this case, for example, a PET unit can be arranged directly downstream of an MRT unit. The PET is therefore performed after the MRT. Thus, the patient is conveyed, for example, on a couch, from the MRT unit to the PET unit. The two units are consequently separated from one another in space, and the two imaging methods therefore take place independently of one another, consecutively in time.
A diagnostic MRT unit with an examination space is disclosed in DE 44 14 371 C2. The MRT unit in this case comprises a high frequency antenna device and a gradient coil system, the high frequency antenna device being arranged nearer to the examination space than the gradient coil system. A high frequency shield in the shape of the lateral surface of a cylinder is arranged in this case between the gradient coil system and high frequency antenna device.
EP 0 141 383 B1 and EP 0 177 855 B1 specify exemplary embodiments of high frequency antenna devices for MRT units by which a homogeneous magnetic field can be generated in conjunction with a signal sensitivity of uniform nature. Such high frequency antenna devices are also termed bird cage antenna among experts.